Modulation



- May 7, 19.25.- o. Ban-1M1 Y -2.000,111

' MODULATION Filed Oct. 27, 195:5

5 ggwlkgk INVENTOR' ATTORNEY A The. present invention relates to modulated transmitters and in particular to telephonytrans- .HIt isknowninthe artvthat'inuorder to-insure current economy .inlthe operationfof'aa telephony transmitter; said telephony transmitter imaytbe operated in such' a mannerthat themean carrier wave..amplitudel is changed in accordance with changes in the volume of the speech or music to be impressed thereon and that the modulated waves-as transmitted areof an approximately constant degree of modulation with respect to time. To accomplishthisit is possible, for in-- stance, to use transmitter circuits'in which the anode direct current potential supplying the final stage serving asthemodulating stage is cone trolled. Such an arrangement has two favorable features, the first of whichisthat, when the amplitude of the modulating frequency decreases the mean amplitude of the produced carrier wave is reduced dueto the simultaneous decrease of the direct anodecurrent potential. In addition in decreasingihe. direct anode potential, the

anode losses are likewise reduced due to' the decrease in the anode zero or no modulation current.

For this known method in the controlled stage,

only tubes having a large durchgriff (through grip of the plate on the electrons between grid and cathode) i are suitable,'the modulated tubes oscillate at reduced tension, meaning the alternating voltage amplitude superposed upon the, anode potential is always small as compared withthe anode direct current potential, and the change ofthe direct current anode potential'in tubes having a small (reciprocal of the amplification durchgriif factor) would not cause an appreciable variation of the high frequency amplitude. It is merely due, to'

to have a large amplification factor reciprocal,

in order to obtain at changing anode potential an effective action upon the high frequency current. Thus in the hitherto known arrangements H t t -Drahflm frelcxranh e I m. b. I1., l 3 ei-lin, gel-maria; a corporation, of r "1 1 ,;:;Application meta-21.1 9

whic aimed-at a wide control fof tlie, amplitude of thecarner wave. tubes hav ing-a largefampli fication' factor were 1 of necessity. On th'efother hand me niethod of 'transmitting waves or .511 pro'ximatelycoiistant degree" of modulation with a controlled carrier wave the; disadvantage "J that if it?tlc'ie's 'not operate over -the entire modu lationranfgefwitli buta 'srnall control ofithe arrier 1 wave which 5 man control', however, i mp: posed to the desired effect of current economy, the v receiver used'to demodulate said controlled wave is required to be substantially. distortionless in operation. Such transmitter can ordinarily only be received with strong distortion.

According to the present invention in order" to obtain an'economically operated transmitter the aim is,fin th'efirst placefto avoid anode losses instead of effecting radiation of waves of constant invention ;the power amplifier tubes primarily used in'the transmitter output stage consist of high gaintubes having a small .tor reciprocal amplification fac- (below 5%). andthe direct current anode potential for these tubes iscontrolled according to the a respective amplitude of the modulation oscillations. The use of tubes having a small amplifica- 1- tion factor reciprocal in transmitter output stages is known as such but it becomes of novel technical I importance in connection with the variationof the direct anode potential controlled by the sound intensity of the modulation. The control of the supplied direct current voltage suitably obf I tained by using rectifiersprovided with control, electrodes and which produce the anode .poten tial byrectifying energy from an alternating current source. The control electrodes, in order to vary the supplied current voltage, are'iinfluenced potentials.

ment of the invention by wayof example.

' in'accordance withthe amplitude of modulation" l mitter oscillations are supplied from the output.

circuit of the transmitter tube E. The tubeE re- 1 ceives the high frequency control oscillations 50,

from a high frequency source H. The anode of the tube E is fed'by direct current potential. The direct current anode potential is producedby means of a transformer T connected with a source of alternating current on the one .hand

and to a rectifier tubeG provided i ha control 5'5 to supply modulating currents from the source M to thevgrid of the tube E. The primary winding of T2 is coupled to the microphone circuit Ml-r Furthermore, parallel to the secondary winding of the transformer T2 a rectifier tube K has'its ;ti'on factor reciprocal, a source of high frequency anode to cathode impedanceiconnected-in series with a blocking condenser C(bridged by a reels Under the influence o!- the i'r'iodulating 1T currents voltages are produced at the condenser C4, the value of which corregponds-yvitnthei voltage of the audio frequency currcnts iiThesez; voltages on the one hand are supplied to thetgiid, electrode of a tube V operating in the bend'por-" tor R.

tion ofits characteristic, The anode pithetube V is likewise fe 'fromthe; ine transformer; '1:

may be of the type in which initiation of current flow is dependent on grid potential reaching a certain value, continues irrespective of grid potential changes, and is terminated only by falling of! of anode potential below a predetermined value.

-Ha vingthus.described my invention and the operation thereonwhat I claim is: In a telephony signalling system, a thermionic tube having anode electrode, control grid electrode, screen-like electrode and cathode electrode, said tube when energized having a low amplificaoscillations connected with the control grid electrode of said tube, a source of modulating potentials connectedwith the control grid of said tube,

and means for maintaining a desired relation beutween the amplitude of the high frequency waves ,and of the .modulating potentials to control the degree of modulation including a rectifier of the controllable type connected at its input to a source of alternatingv current and" at its output to the anode and screen-like and cathode electrodes of said tube to energize the same and a circuit energized by modulating potentials connected with said'rectifier for controlling the rectifying action thereof.

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